Question

how does water remains cool in a earthen pot?

Answer 1

An earthenware pot is porous and the water soaks into it and eventually gets to the exterior surface of the pot where it starts to evaporate; this evaporation takes energy to occur and this depresses the temperature of the pot overall, thereby cooling the contents

Answer 2

Water looses its temperature through small pores present in the pot. Hence in an earthen pot (matka) become cool during summer.